1. Field of the Invention
This invention relates to a heartbeat synchronous information acquiring apparatus for determining heartbeat synchronous information based on an impedance pulse wave of a living body. The present information also relates to a pulse wave propagation velocity related information acquiring apparatus, a blood pressure monitoring apparatus and a preejection period measuring apparatus adapted to utilize the acquired heartbeat synchronous information. As far as this patent application is concerned, the expression xe2x80x9cheartbeat synchronous informationxe2x80x9d refers to a predetermined part of a heartbeat synchronous pulse wave.
2. Detailed Description of the Related Art
The impedance between two bodily positions with the heart interposed between them involves changes in the impedance attributable to expansions and contractions of the heart that are expressed in the form of an impedance pulse wave composed of heartbeat synchronous components. Apparatus for acquiring various pieces of bio-information by utilizing the heartbeat synchronous information determined as a function of the impedance pulse wave have been proposed to date.
For instance, the applicant of the present patent application has proposed in Japanese Patent Application No. 8-142597 an apparatus for determining heartbeat synchronous information as a function of the impedance pulse wave of a living body and measuring the pulse wave propagation velocity at which a pulse wave propagates in a living body by utilizing the obtained heartbeat synchronous information. Additionally, the applicant of the present patent application has proposed in Japanese Patent Application No. 8-142596 a blood pressure monitoring apparatus for determining heartbeat synchronous information as a function of the impedance pulse wave of a living body, continually computing the pulse wave propagation velocity at which the pulse wave propagates in a living body by utilizing the obtained heartbeat synchronous information and then monitoring a blood pressure based on the obtained pulse wave propagation velocity. Furthermore, the applicant of the present patent application has proposed in Japanese Patent Application No. 8-142598 a preejection period measuring apparatus for computing a preejection period from a time lag between a predetermined part of an induced electro-cardiac wave and a corresponding predetermined part of the impedance pulse wave (or heartbeat synchronous information) of a living body.
When acquiring various pieces of bio-information by utilizing the heartbeat synchronous information determined as a function of the impedance pulse wave of a living body, it is absolutely essential that the heartbeat synchronous information is determined accurately. However, the impedance of a living body is in fact a micro-signal that needs to be amplified by about 10,000 times (to about 80 dB) when it is to be perceived as a signal. As the micro-signal is amplified, induction noise surrounding a subject and radiation noise from unrelated devices become apparent making the signal less recognizable. Additionally, the blood of the subject moving through blood vessels can give rise to noise along with the impedance pulse wave. Furthermore, the impedance can change as the subject moves, which in turn moves electrodes fitted to the subject. Therefore, the noise detected along with the impedance pulse wave can sometimes make it impossible to accurately determine the heartbeat synchronous information of the subject. For instance, when determining the heartbeat synchronous information from consecutive peaks of heartbeats in the impedance pulse wave, the amplitudes of the peaks of high noise can be greater than those of the peaks of the heartbeats. Consequently, noise which shows a large amplitude can be determined as heartbeat synchronous information.
In view of the above identified circumstances, the object of the present invention is to provide a heartbeat synchronous information acquiring apparatus that can accurately determine heartbeat synchronous information as well as a pulse wave propagation velocity related information acquiring apparatus, a blood pressure monitoring apparatus, and a preejection period measuring apparatus adapted to utilize the acquired heartbeat synchronous information.
As a result of intensive research efforts carried but to achieve the above object, the inventor of the present invention has found that it is possible to accurately determine the heartbeat synchronous information by extracting an impedance pulse wave for a predetermined period, which is a time span long enough to generate such heartbeat synchronous information, out of a continuously detected impedance pulse wave. This is done by using an induced electro-cardiac wave adapted to produce a signal greater than a signal of an impedance of a living body, and hence less affected by noise. The heartbeat synchronous information is then determined from an extracted partial impedance pulse wave because the heartbeat synchronous information is not affected by noise other than that of the extracted part. This invention is based on this finding.
The First Aspect of the Invention
In the first aspect of the invention, there is provided a heartbeat synchronous information acquiring apparatus provided with an impedance pulse wave detector for detecting an impedance pulse wave of a living body, containing heartbeat synchronous components, between a pair of electrodes fitted to predetermined positions of the living body with the heart interposed between them. This is done in order to acquire the heartbeat synchronous information, generated synchronously with heartbeats of the living body, based on the impedance pulse wave. The apparatus is composed of (a) an induced electro-cardiac wave detection device for continuously detecting an induced electro-cardiac wave of the living body, and (b) a gate means for extracting a partial impedance pulse wave from the impedance pulse wave by taking in the impedance pulse wave for an intake period based on a time of detection of a predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device. There is also (c) a heartbeat synchronous information determining means for determining a periodically appearing predetermined part of the partial impedance pulse wave extracted by the gate means as heartbeat synchronous information.
Advantages the First Aspect of the Invention
With the above described arrangement, the partial impedance pulse wave is extracted by the gate means from the impedance pulse wave. The partial impedance pulse wave is detected by the impedance pulse wave detector by taking in the impedance pulse wave for the intake period based on the time of detection of the predetermined part of the induced electro-cardiac wave. The periodically appearing predetermined part of the partial impedance pulse wave extracted by the gate means is determined as heartbeat synchronous information by the heartbeat synchronous information determining means. Thus, it is now possible to accurately acquire heartbeat synchronous information.
Other Modes of Carrying out the Invention in the First Aspect
Preferably, the intake period of the gate means is from the end of a predetermined first time period starting from the time of detection of the predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device to the end of a predetermined second time period starting from the time of detection of the predetermined part. The second time period is longer than the first time period. With this arrangement, the intake period is determined only based on a part of the induced electro-cardiac wave that is less affected by noise so that the intake period can be determined accurately, and it is no longer necessary to provide an additional device for determining the intake period. It will be appreciated that, if the intake period is not determined accurately, the partial impedance pulse wave may contain unnecessary parts, or may not contain the necessary part, which is the heartbeat synchronous information.
Preferably, the heartbeat synchronous information acquiring apparatus is further composed of a light source for irradiating the skin of the living body with light, a photo detector for detecting transmitted or reflected light originating from the light source, and a photoelectric pulse wave sensor for detecting the photoelectric pulse wave at a bodily part irradiated with light emitted from the light source. The intake period of the gate means is from the end of the first time period starting from the time of detection of the predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device to the time of detection of the predetermined part of the photoelectric pulse wave by the photoelectric pulse wave sensor. With this arrangement, the end of the intake period can be determined accurately because the photoelectric pulse wave detected by the photoelectric pulse wave sensor is largely free of electromagnetic noise. It will be appreciated that, if the intake period is not determined accurately, the partial impedance pulse wave may contain unnecessary parts, or may not contain the necessary part, which is the heartbeat synchronous information.
The Second Aspect of the Invention
In the second aspect of the invention, there is provided a blood pressure monitoring apparatus for monitoring the blood pressure of a living body. The apparatus is composed of (a) a blood pressure measuring means for measuring the blood pressure of the living body by using a cuff for pressing the artery of the living body, and (b) an induced electro-cardiac wave detection device for continuously detecting an induced electro-cardiac wave of said living body. There is also (c) an impedance pulse wave detector, for detecting an impedance pulse wave of a living body containing heartbeat synchronous components, between a pair of electrodes fitted to predetermined positions of the living body with the heart interposed between them, (d) a gate means for extracting a partial impedance pulse wave from the impedance pulse wave by taking in the impedance pulse wave for an intake period based on a time of detection of a predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device, and (e) a pulse wave detector fitted to a part of the living body for detecting a pulse wave propagating through the artery of the living body In addition there is (f) a pulse wave propagation velocity related information computing means for continually computing information on a pulse wave propagation velocity based on the partial impedance pulse wave and the pulse wave propagating through the artery of the living body, and (g) a propagation velocity related information versus blood pressure relationship determining means for determining the relationship between propagation velocity related information computed by the pulse wave propagation velocity related information computing means and a blood pressure measured by the blood pressure measuring means at each time of such measurement. Also there is (h) a monitored blood pressure determining means for continually determining a value of the monitored blood pressure from the corresponding relationship between the propagation velocity related information and the blood pressure as determined by the propagation velocity related information versus blood pressure relationship determining means based on the actual pulse wave propagation velocity related information computed by the pulse wave propagation velocity related information computing means.
Advantages of the Second Aspect of the Invention
With the above described arrangement, each time the blood pressure is measured by the blood pressure measuring means, the propagation velocity related information versus blood pressure relationship determining means determines the corresponding relationship between the propagation velocity related information computed by the pulse wave propagation velocity related information computing means and the blood pressure measured by the blood pressure measuring means. The monitored blood pressure determining means continually determines the value of the monitored blood pressure from the corresponding relationship between the propagation velocity related information and the blood pressure. The blood pressure is determined by the propagation velocity related information versus blood pressure relationship determining means based on the actual pulse wave propagation velocity related information computed by the pulse wave propagation velocity related information computing means. The pulse wave propagation velocity related information computed by the pulse wave propagation velocity related information computing means is accurate because it is computed based on the partial impedance pulse wave taken in only in the intake period as determined by the gate means based on the time of detection of the predetermined part of the induced electro-cardiac wave. Therefore the value of the monitored blood pressure is highly reliable because it is continually determined by the monitored blood pressure determining means based on the accurate pulse wave propagation velocity related information.
Other Modes of Carrying out the Invention in the Second Aspect
Preferably, the blood pressure monitoring apparatus further includes a monitored blood pressure abnormality judging means for judging the normality or abnormality of the value of the monitored blood pressure as determined by said monitored blood pressure determining means. This is done by referring to a predetermined judgment reference range and triggering the operation of the blood pressure measuring means when the value of the monitored blood pressure is judged to be an abnormal value. With this arrangement, whenever the value of the monitored blood pressure is judged to be an abnormal value, an operation of measuring the blood pressure, using a cuff, is carried out immediately by the blood pressure measuring means and the corresponding relationship between the propagation velocity related information and the blood pressure is determined for another time by the propagation velocity related information versus blood pressure relationship determining means. Therefore, an updated and hence reliable blood pressure value is automatically obtained by means of the cuff whenever an abnormal value is observed for the monitored blood pressure so improving the reliability of the succeeding operation of monitoring the blood pressure.
Preferably, the blood pressure monitoring apparatus further includes a display for showing the trend of the monitored blood pressure values that are continually determined by the monitored blood pressure determining means. With this arrangement, the trend in the changes in the blood pressure that have been observed can be accurately recognized so making the doctor""s diagnosis easier and more accurate.
Preferably, the display is adapted to show an alarm for whenever the monitored blood pressure value is judged to be abnormal by the monitored blood pressure abnormality judging means. With this arrangement, by way of the alarm, the operator/doctor is reliably made aware of an abnormal condition of the living body or, at least, an abnormal condition of the blood pressure monitoring apparatus.
Preferably, the pulse wave detector is composed of the cuff which is wound around a living body and a cuff pulse wave discriminating circuit for extracting a cuff pulse wave that is a pressurized vibration of the cuff. With this arrangement, if the pulse wave detector is used with the blood pressure measuring apparatus, the cuff of the blood pressure measuring apparatus can be shared with the pulse wave detector for the purpose of pulse wave detection. This arrangement is a great advantage in terms of cost and simplicity.
Preferably, the pulse wave detector is composed of a pressure pulse wave sensor for detecting a pressure pulse wave that is generated in the artery of the living body as the artery is pressed via the skin of the living body. With this arrangement, particularly when it is used with a continuous blood pressure measuring apparatus for continuously measuring an arterial pressure by detecting the pressure pulse wave of the radial artery by means of the pressure pulse wave sensor, the pressure pulse wave sensor of the continuous blood pressure measuring apparatus can be shared by the pulse wave detector to reduce the cost of the latter.
The Third Aspect of the Invention
In the third aspect of the invention, there is provided a blood pressure monitoring apparatus provided with a blood pressure measuring means for measuring the blood pressure of a living body by periodically shifting a pressure of a cuff that is fitted to and pressing against the living body in a predetermined cycle based on a pulse synchronous wave generated in the process of shifting the pressure pressing against the living body. The apparatus is composed of (a) an electro-cardiac wave detection device for continuously detecting an induced electro-cardiac wave of the living body, and (b) an impedance pulse wave detector, for detecting an impedance pulse wave of the living body containing heartbeat synchronous components, between a pair of electrodes fitted to predetermined positions of the living body with the heart interposed between them. There is also (c) a gate means for extracting a partial impedance pulse wave from the impedance pulse wave by taking in the impedance pulse wave for an intake period based on a time of detection of a predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device, and (d) a pulse wave detector fitted to a part of the living body for detecting a pulse wave propagating through an artery of the living body. In addition there is (e) a pulse wave propagation velocity related information computing means for continually computing information on a pulse wave propagation velocity based on the partial impedance pulse wave and the pulse wave propagating through the artery of the living body, and (f) a monitored blood pressure change judging means for judging a change in a blood pressure of the living body based on any change in the pulse wave propagation velocity related information, continually computed by the pulse wave propagation velocity related information computing means, which exceeds a predetermined judgment reference value.
Advantages of the Third Aspect of the Invention
With the above described arrangement, a change in the blood pressure of the living body is judged by the monitored blood pressure change judging means based on any change in the pulse wave propagation velocity related information, continually computed by the pulse wave propagation velocity related information computing means, which exceeds the predetermined judgment reference value. The pulse wave propagation velocity related information computed by the pulse wave propagation velocity related information computing means is accurate and highly reliable because it is computed based on the partial impedance pulse wave taken in only in the intake period. The partial impedance pulse wave taken in only in the intake period is determined by the gate means based on the time of detection of the predetermined part of the induced electro-cardiac wave and the judgment on the change in the blood pressure of the living body that is done by the monitored blood pressure change judging means based on the accurate pulse wave propagation velocity related information.
Other Modes of Carrying out the Invention in the Third Aspect
Preferably, the monitored blood pressure change judging means is adapted to trigger the operation of the blood pressure measuring means when it judges a change in the blood pressure of the living body to be abnormal. Then, whenever it is judged by the monitored blood pressure change judging means that an abnormal condition exists with respect to the blood pressure of the living body, an operation of measuring the blood pressure, using the cuff, is carried out immediately by the blood pressure measuring means. Therefore, an updated and hence reliable blood pressure value is automatically obtained by means of the cuff at the time of judgment on the change in the blood pressure of the living body.
Other Modes of Carrying out the Invention in the Second and Third Aspects
Preferably, the intake period of the gate means of the blood pressure monitoring apparatus is from the end of a predetermined first time period, starting from the time of detection of the predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device, to an end of a predetermined second time period, starting from the time of detection of the predetermined part. The second time period is longer than the first time period. With this arrangement, the intake period is determined only based on a part of the induced electro-cardiac wave that is less affected by noise so that the intake period can be determined accurately, and it is no longer necessary to provide an additional device for determining the intake period.
Preferably, the pulse wave detector includes a photoelectric pulse wave sensor for detecting a photoelectric pulse wave at a bodily part irradiated with light which includes a light source for irradiating the skin of the living body with light and a photodetector for detecting transmitted or reflected light originating from the light source. The intake period of the gate means is from the end of the first time period, starting from the time of detection of the predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device, to the time of detection of the predetermined part of the photoelectric pulse wave by the photoelectric pulse wave sensor. With this arrangement, pulse wave propagation velocity related information can be continually computed by the pulse wave propagation velocity related information computing means based on the partial impedance pulse wave and the photoelectric pulse wave. The end of the intake period during which the impedance pulse wave is taken in by the gate means is determined based on the photoelectric pulse wave so that the photoelectric pulse wave sensor for computing the pulse wave propagation velocity related information can also be advantageously used for determining the end of the intake period. The intake period can be determined accurately because the photoelectric pulse wave detected by the photoelectric pulse wave sensor is largely free of electromagnetic noise.
Preferably, the impedance pulse wave detector of the blood pressure monitoring apparatus includes an impedance detector for detecting an impedance of the living body between the two electrodes, fitted to predetermined positions of the living body, with the heart of the living body interposed between them. There is also an impedance pulse wave discriminator for discriminating the impedance pulse wave, containing heartbeat synchronous components, from the impedance of the living body detected by the impedance detector. The impedance obtained by way of the pair of electrodes, fitted to predetermined positions of the living body with the heart interposed between them, includes a respiration impedance wave that changes synchronously with a respiration of the living body and the impedance pulse wave that changes synchronously with the heartbeat of the living body. The respiration impedance wave and the impedance pulse wave are laid one on top of the other so that the impedance pulse wave can be easily isolated to the great advantage of the apparatus.
Preferably, the pulse wave detector is composed of a photoelectric pulse wave sensor including a light source for emitting rays of red light or infrared rays adapted to be reflected by hemoglobin toward the skin of the living body, and a photo detector for detecting transmitted or reflected rays of red light or infrared rays originating from the light source. With this arrangement, when the photoelectric pulse wave sensor is used with a pulse oximeter which includes a photoelectric pulse wave sensor for detecting the pulse wave by using light showing two wavelengths for irradiation, the photoelectric pulse wave sensor of the pulse oximeter can be shared by the pulse wave detector to reduce the cost of the latter.
The Fourth Aspect of the Invention
In the fourth aspect of the invention, there is provided a pulse wave propagation velocity related information acquiring apparatus for acquiring information relating to a propagation velocity of a pulse wave propagating through an artery of a living body. The apparatus is composed of (a) an electro-cardiac wave detection device for continuously detecting an induced electro-cardiac wave of the living body, and (b) an impedance pulse wave detector for detecting an impedance pulse wave of the living body, containing heartbeat synchronous components, between a pair of electrodes fitted to predetermined positions of the living body with the heart interposed between them. There is also (c) a gate means for extracting a partial impedance pulse wave from the impedance pulse wave by taking in the impedance pulse wave for an intake period based on the time of detection of a predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device, and (d) a pulse wave detector fitted to a part of the living body for detecting the pulse wave propagating through the artery of the living body. In addition there is (e) a pulse wave propagation velocity related information computing means for computing information on the velocity of the pulse wave propagating through the living body based on a time difference obtained by subtracting a second time difference from a first time difference. The first time difference is computed as the time difference between a time a predetermined part in the induced electro-cardiac wave detected by the induced electro-cardiac wave detection device periodically appears and a time a predetermined part in the pulse wave detected by the pulse wave detector periodically appears. The second time difference is computed as the time difference between a time the predetermined part in the induced electro-cardiac wave periodically appears and a time a predetermined part in the partial impedance pulse wave extracted by the gate means periodically appears.
Advantages of the Fourth Aspect of the Invention
With the above described arrangement, the partial impedance pulse wave is extracted by the gate means from the impedance pulse wave detected by the impedance pulse wave detector by taking in the impedance pulse wave for an intake period based on the time of detection of the predetermined part of the induced electro-cardiac wave. The pulse wave propagation velocity related information computing means computes the first time difference which is the time difference between the time the predetermined part in the induced electro-cardiac wave detected by the induced electro-cardiac wave detection device periodically appears and the time the predetermined part in the pulse wave detected by the pulse wave detector periodically appears. The pulse wave propagation velocity related information computing means computes the second time difference which is the time difference between the time the predetermined part in the induced electro-cardiac wave periodically appears and the time the predetermined part in the partial impedance pulse wave extracted by the gate means periodically appears. Then, the pulse wave propagation velocity related information computing means computes information on the velocity of the pulse wave propagating through the living body based on the time difference obtained by subtracting the second time difference from the first time difference. In other words, the second time difference is computed by using the periodically appearing predetermined part of the impedance pulse wave that is relatively free from noise and therefore accurate. Then, the pulse wave propagation velocity related information is computed based on the accurate second time difference and therefore it is accurate and reliable.
The Fifth Aspect of the Invention
In the fifth aspect of the invention, there is provided a pulse wave propagation velocity related information acquiring apparatus for acquiring information relating to a propagation velocity of a pulse wave propagating through an artery of a living body. The apparatus is composed of (a) an electro-cardiac wave detection device for continuously detecting an induced electro-cardiac wave of the living body, and (b) an impedance pulse wave detector for detecting an impedance pulse wave of the living body, containing heartbeat synchronous components, between a pair of electrodes fitted to predetermined positions of the living body with the heart interposed between them. There is (c) a gate means for extracting a partial impedance pulse wave from the impedance pulse wave by taking in the impedance pulse wave for an intake period based on a time of detection of a predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device, and (d) a pulse wave detector fitted to a part of the living body for detecting the pulse wave propagating through the artery of the living body. In addition there is (e) a pulse wave propagation velocity related information computing means for computing information on a velocity of the pulse wave propagating through the living body based on a time difference between a time a predetermined part in the partial impedance pulse wave extracted by the gate means periodically appears and a time a predetermined part in the pulse wave detected by the pulse wave detector periodically appears.
Advantages of the Fifth Aspect of the Invention
With the above described arrangement, the partial impedance pulse wave is extracted by the gate means from the impedance pulse wave detected by the impedance pulse wave detector by taking in the impedance pulse wave for the intake period based on the time of detection of a predetermined part of the induced electro-cardiac wave. The pulse wave propagation velocity related information computing means computes information on the pulse wave propagation velocity based on the time difference between the time the predetermined part in the partial impedance pulse wave extracted by the gate means periodically appears and the time the predetermined part in the pulse wave detected by the pulse wave detector periodically appears. In other words, the time difference is computed by using the periodically appearing predetermined part of the impedance pulse wave that is relatively free from noise as a starting point and therefore it is accurate. Then, the pulse wave propagation velocity related information is computed based on the accurate time difference and therefore it is accurate and reliable.
Other Modes of Carrying out the Invention in the Fourth and Fifth Aspects
Preferably, the impedance pulse wave detector of the pulse wave propagation velocity related information acquiring apparatus includes an impedance detector for detecting the impedance of the living body between the two electrodes fitted to predetermined positions of the living body with the heart of the living body interposed between them, and an impedance pulse wave discriminator for discriminating the impedance pulse wave containing heartbeat synchronous components from the impedance of the living body detected by the impedance detector. The impedance, obtained by way of the pair of electrodes fitted to predetermined positions of the living body with the heart interposed between them, includes a respiration impedance wave that changes synchronously with a respiration of the living body and an impedance pulse wave that changes synchronously with the heartbeat of the living body. The respiration impedance wave and the impedance pulse wave are laid one on top of the other so that the impedance pulse wave can be easily isolated to the great advantage of the apparatus.
Preferably, the pulse wave detector is composed of a cuff to be wound around the living body and a cuff pulse wave discriminating circuit for extracting a cuff pulse wave that is a pressurized vibration of the cuff. With this arrangement, if the pulse wave detector is used with a blood pressure measuring apparatus, the cuff of the blood pressure measuring apparatus can be shared by the pulse wave detector for the purpose of pulse wave detection. This arrangement has a great advantage in terms of cost and simplicity.
Preferably, the pulse wave detector includes a pressure pulse wave sensor for detecting a pressure pulse wave that is generated in the artery of the living body as the artery is pressed via the skin of the living body. With this arrangement, particularly when it is used with a continuous blood pressure measuring apparatus for continuously measuring an arterial pressure by detecting the pressure pulse wave of a radial artery by means of the pressure pulse wave sensor, the pressure pulse wave sensor of the continuous blood pressure measuring apparatus can be shared by the pulse wave detector to reduce the cost of the pulse wave detector.
Preferably, the pulse wave detector is composed of a photoelectric pulse wave sensor, including a light source for irradiating the skin of the living body with rays of light, and a photo detector for detecting transmitted or reflected rays of light originating from the light source. With this arrangement, when it is used with a pulse oximeter which includes a photoelectric pulse wave sensor for detecting the pulse wave by using light showing two wavelengths for irradiation, the photoelectric pulse wave sensor of the pulse oximeter can be shared by the pulse wave detector to reduce the cost of the pulse wave detector.
Preferably, the intake period of the gate means of the pulse wave propagation velocity related information acquiring apparatus is from the end of a predetermined first time period, starting from the time of detection of the predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device, to the end of a predetermined second time period, starting from the time of detection of the predetermined part. The second time period is longer than the first time period. With this arrangement, the intake period is determined only based on a part of the induced electro-cardiac wave that is less affected by noise. Therefore, the intake period can be determined accurately and it is no longer necessary to obtain any additional information for determining the intake period.
Preferably, the pulse wave propagation velocity related information acquiring apparatus includes the photoelectric pulse wave sensor as the pulse wave detector. It is also preferable that the intake period of the gate means is from the end of the first time period, starting from the time of detection of the predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device, to the time of detection of the predetermined part of the photoelectric pulse wave by the photoelectric pulse wave sensor. With this arrangement, the end of the intake period for the gate means to read the impedance pulse wave is determined based on the photoelectric pulse wave. Therefore, the photoelectric pulse wave sensor for computing the pulse wave propagation velocity related information can also be used for determining the end of the intake period. The end of the intake period can be determined accurately because the photoelectric pulse wave detected by the photoelectric pulse wave sensor is largely free of electromagnetic noise.
The Sixth Aspect of the Invention
In the sixth aspect of the invention, there is provided a preejection period measuring apparatus for measuring a preejection period from the start of a contraction of the heart of a living body to the time when blood is ejected out from the heart by the heartbeat. The apparatus is composed of (a) an electro-cardiac wave detection device for detecting an induced electro-cardiac wave of the living body, and (b) an impedance pulse wave detector for detecting an impedance pulse wave of a living body containing heartbeat synchronous components between a pair of electrodes fitted to predetermined positions of the living body with the heart interposed between them. There is also (c) a gate means for extracting a partial impedance pulse wave from the impedance pulse wave by taking in the impedance pulse wave for an intake period as determined based on the time of detection of a predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device, and (d) a pulse wave detector fitted to a part of the living body for detecting a pulse wave propagating through an artery of the living body. In addition there is (f) a preejection period computing means for computing the preejection period by subtracting a second time difference from a first time difference. The first time difference is computed as the time difference between a time a predetermined part in the induced electro-cardiac wave detected by the induced electro-cardiac wave detection device periodically appears and a time a predetermined part in the pulse wave detected by the pulse wave detector periodically appears. The second time difference is computed as the time difference between a time a predetermined part in partial impedance pulse wave extracted by the gate means periodically appears and a time the predetermined part in the pulse wave detected by the pulse wave detector periodically appears.
Advantages of the Sixth Aspect of the Invention
With the above described arrangement, the partial impedance pulse wave is extracted by the gate means from the impedance pulse wave detected by the impedance pulse wave detector by taking in the impedance pulse wave for the intake period as determined based on the time of detection of the predetermined part of the induced electro-cardiac wave. The preejection period computing means computes the first time difference which is the time difference between the time the predetermined part in the induced electro-cardiac wave detected by the induced electro-cardiac wave detection device periodically appears and the time the predetermined part in the pulse wave detected by the pulse wave detector periodically appears. The preejection period computing means also computes the second time difference which is the time difference between the time the predetermined part in partial impedance pulse wave extracted by the gate means periodically appears and the time the predetermined part in the pulse wave detected by the pulse wave detector periodically appears, and then computes the preejection period by subtracting the second time difference from the first time difference. In other words, the second time difference is computed by using as a starting point the periodically appearing predetermined part of the impedance pulse wave that is relatively free from noise, and therefore it is accurate. Then, the preejection period is computed by subtracting the accurate second time difference from the first time difference, and therefore it is accurate and reliable.
The Seventh Aspect of the Invention
In the seventh aspect of the invention, there is provided a preejection period measuring apparatus for measuring a preejection period from the start of a contraction of the heart of a living body to a time when blood is ejected out from the heart by the heartbeat. The apparatus is composed of (a) an electro-cardiac wave detection device for detecting an induced electro-cardiac wave of the living body, and (b) an impedance pulse wave detector for detecting an impedance pulse wave of the living body between a pair of electrodes fitted to predetermined positions of the living body with the heart interposed between them. There is also (c) a gate means for extracting a partial impedance pulse wave from the impedance pulse wave by taking in the impedance pulse wave for an intake period as determined based on a time of detection of a predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device. In addition there is (d) a preejection period computing means for computing the preejection period as a time difference between a time a predetermined part in the induced electro-cardiac wave detected by the electro-cardiac wave detection device periodically appears and a time a predetermined part in the partial impedance pulse wave extracted by the gate means periodically appears.
Advantages of the Seventh Aspect of the Invention
With the above described arrangement, the partial impedance pulse wave is extracted by the gate means from the impedance pulse wave detected by the impedance pulse wave detector by taking in the impedance pulse wave for the intake period as determined based on the time of detection of the predetermined part of the induced electro-cardiac wave. The preejection period computing means computes the preejection period as the time difference between the time the predetermined part in the induced electro-cardiac wave detected by the electro-cardiac wave detection device periodically appears and the time the predetermined part in the partial impedance pulse wave extracted by the gate means periodically appears. In other words, the preejection period is computed by using as a terminating point a periodically appearing predetermined part of the impedance pulse wave that is relatively free from noise, and therefore accurate. According to the seventh aspect of the invention, since a microphone for detection the cardiac operation of beating out blood is not used, the preejection period can be measured accurately if the heart sound contains noises.
Other Modes of Carrying out the Invention in the Sixth and Seventh Aspects
Preferably, the preejection period measuring apparatus further includes a cardiac function assessing means for assessing a cardiac function of the living body based on the preejection period computed by the preejection period computing means. With this arrangement, the cardiac function can be assessed accurately when compared with the assessment of the cardiac function conducted based on the preejection period determined by using a microphone.
Preferably, the intake period of the gate means of the preejection period measuring apparatus is from the end of a predetermined first time period starting from the time of detection of the predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device to the end of a predetermined second time period starting from the time of detection of the predetermined part. The second time period is longer than the first time period. With this arrangement, the intake period is determined only based on a part of the induced electro-cardiac wave that is less affected by noise so that the intake period can be determined accurately, and it is no longer necessary to obtain any additional information for determining the intake period.